Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$181.40	10.552%	$200.5413	$200.54	$200.55	$200.50
Purchase #2	$119.51	6.691%	$127.5064	$127.51	$127.50	$127.50
Purchase #3	$133.68	8.848%	$145.508	$145.51	$145.50	$145.50
Purchase #4	$45.85	11.664%	$51.1979	$51.20	$51.20	$51.20
Purchase #5	$98.98	5.427%	$104.3516	$104.35	$104.35	$104.40
Purchase #6	$131.73	5.817%	$139.3927	$139.39	$139.40	$139.40
Purchase #7	$200.97	10.540%	$222.1522	$222.15	$222.15	$222.20
7 purchase totals =	$912.12		$990.6501	$990.65	$990.65	$990.70